CheatSheetForSizeOfVariablesInC.md

variableSizeAndRange.md

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[TOC]

Data Types

There are four data types in C language. They are,

Types	Data Types
Basic data types	int, char, float, double
Derived data type	pointer*, array [], struct, union
Void data type	void
Enumeration data type	enum

Types, Specifiers and Qualifiers

Data Type	Storage Class Specifier	Modifier/Specifier	Type Qualifier	Composite
int	extern (global)	short	volatile	array []
char	static	signed, unsigned	const	struct
float	auto	long		union
double	register	long long
pointer*	typedef *
void

Valid combinations

char, signed char, unsigned char
int, signed int, unsigned int
short int, signed short int, unsigned short int
long int, signed long int, unsigned long int
float, double, long double

###Minimum Type Limits

Any compiler conforming to the Standard must also respect the following limits with respect to the range of values any particular type may accept. Note that these are lower limits: an implementation is free to exceed any or all of these. Note also that the minimum range for a char is dependent on whether or not a char is considered to be signed or unsigned.

Minimum Range Table

Type	Minimum Range
signed char	-127 to +127
unsigned char	0 to 255
short int	-32767 to +32767
int	-32767 to +32767
unsigned short int	0 to 65535
unsigned int	0 to 65535
long int	-2147483647 to +2147483647
unsigned long int	0 to 4294967295

Minimum Precision Table

Type	Minimum Precision	Remarks
float	6 digits	observed at 8 digits
double	10 digits	observed at 17 digits
long double	10 digits	observed at 20 digits

The Standard also specifies that these limits should be present as preprocessor macros in the header file <limits.h>

Size and Range of Variable Types in C

For a 16-bit operating system, here's a parital tabulation borrowed from this :

Modifier	Variable Type	sizeof	Range	Precision
unsigned	char	1	0 to 256
	char	1	-127 to 127
short	int	2	–32,767 to 32,767
	int	2
unsigned	int	2	0 to 65,535
long	int	4	–2,147,483,647 to 2,147,483,647
unsigned long	int	4	0 to 4,294,967,295
long long	int	8	-(2^63 –1) to (2^63 –1)
unsigned long long	int	8	0 to 2^(8bits*8bytes -1) = 2^64 - 1
	float	4	1E-37 to 1E+37	upto 6-9 significant digits e.g. 3.141592 or 3.14159?
	double	8		upto 15-17 significant digits
long	double	10	1E-37 to 1E+37	precision to 10 decimal digits, e.g. 3.1415926535 or 3.141592653?

Quiz

1. A bank opened a banking account for Rangarajan who immediately deposited Rs 40,000. When Rangarajan tried to withdraw the entire amount (Rs 40,000) from the bank's ATM, the ATM terminal refused to issue any money. The reason is:

   • No money in the ATM
   • Erroneous banking software
   • Demonetization (2016) rules until December 31
   • Anyone or all of the above

2. Next morning, the demonetization rules had been relaxed to withdraw up to Rs 50,000. Hearing about this, Rangarajan quickly located another ATM which had cash. Surprisingly, the ATM indicates that the customer had a negative bank balance of Rs -25,536. The reason is:

   • Someone else withdrew all of the money from Rangarajan's account during the previous night
   • The banking software had a bug
   • The computer that powers the ATM has a virus

3. Rangarajan is finally convinced that the bank is using a faulty software. What do you think is the main reason as to why the software is not working properly?

   • The bank software is designed to allow to dispense only small amounts
   • The bank software design adopted the wrong data type for storing customer balances.
   • None of the above

4. Meanwhile, Rangarajan found out that the bank was using a server powered by a 32-bit operating system to run its banking software (built using the C language). A software engineer himself, he got hold off of the source code of the banking software and started reviewing it. Immediately, he found out that the problem (aka software bug) was because of the data type that was used to store the customer bank balance. Which one was it?

   • unsigned int
   • int
   • signed short int
   • float

Programming exercises

Swap nibbles

Write a C program to swap value held by two nibble variables - https://bytes.com/topic/c/answers/650530-nibble-variable

Pointer Snippet

6. Is the following code snippet valid? If yes, explain what the following code snippet is trying to do.

   int *ip;
   ip = (int *)6;
   *ip = 0xFF;

Check Odd or Even

Write a program to check whether a number is odd or even without using the modulo division or multiplication operators?

Sizeof Information

int ≥ 16 bits ≥ size of short
long ≥ 32 bits ≥ size of int    
long long ≥ 64 bits ≥ size of long

No, the standard defines the minimums which for long is 4 bytes and int is 2 bytes. As per the C99 draft standard section 5.2.4.2.1 Sizes of integer types limits.h paragraph 1 says:

[...]Their implementation-defined values shall be equal or greater in magnitude[...]

and for long we have:

 LONG_MIN -2147483647 // -(2^31 - 1)
 LONG_MAX +2147483647 // 2^31 - 1     

which is 4 bytes. For completeness sake, we have the following for int:

 INT_MIN -32767 // -(2^15 - 1)
 INT_MAX +32767 // 2^15 - 1

which is 2 bytes.

sizeof Program for various data types

To run / modify the below program, fork it at http://bit.ly/sizeofC

#include <stdio.h>
#include <limits.h>
int main()
{
   int a;
   char b;
   float c  = 12.34567890123456789;
   double d = 12.34567890123456789;
   printf("Storage size for int data type:     %d \n",sizeof(a));
   printf("Storage size for char data type:    %d \n",sizeof(b));
   printf("Storage size for float data type:   %d \n",sizeof(c));
   printf("Storage size for double data type:  %d \n",sizeof(d));
 
   int* aPointer; 
   void* vPointer; 
   printf("Storage size for int pointer type:  %d\n",sizeof(aPointer));
   printf("Storage size for void pointer type: %d\n",sizeof(vPointer));
 
   short int si; 
   long li;          // same as long int 
   long long lli;    // same as long long int
   long double ld = 12.34567890123456789;
   printf("Storage size for short int type:    %d\n",sizeof(si));
   printf("Storage size for long int type:     %d\n",sizeof(li));
   printf("Storage size for long long int type:%d\n",sizeof(lli));
   printf("Storage size for long double type:  %d\n",sizeof(ld));
 
   float       x  = .12345678901234567891234*10;
   double      z  = .12345678901234567891234*10;
   long double lz = .12345678901234567891234*10;
   printf("x=%f\n", x);
   printf("z=%f\n", z);
   printf("x=  %20.18f\n", x);    // precision to 7-8 significant digits
   // x=  1.234567880630493164
   printf("z=  %20.18f\n", z);    // precision to 14-17 significant digits
   // z=  1.234567890123456690
   printf("lz= %20.18Lf\n", lz);  // precision to 18-20 significant digits
   // lz= 1.234567890123456789
   return 0;
}

Output

Storage size for int data type:     4  // when is it 2? 
Storage size for char data type:    1 
Storage size for float data type:   4 
Storage size for double data type:  8 
Storage size for int pointer type:  4
Storage size for void pointer type: 4
Storage size for short int type:    2
Storage size for long int type:     4
Storage size for long long int type:8
Storage size for long double type:  12
x=1.234568
z=1.234568
x=  1.234567880630493164
z=  1.234567890123456690
lz= 1.234567890123456789

Useful References

http://publications.gbdirect.co.uk/c_book/chapter8/const_and_volatile.html http://www.ericgiguere.com/articles/ansi-c-summary.html